This invention relates to polymers which incorporate castor oil as a copolymerizable component. More specifically, it relates to such polymers having properties ideally adapted for biomedical applications particularly for the fabrication of surgical articles and coatings for surgical articles.
The need to develop suitable coatings for numerous applications, particularly surgical applications, continues unabated. A coating on the surface of a surgical article is often essential for the proper performance of the article. For example, surgical needles typically require that the surface of the needle be coated to reduce the penetration force of the needle when it is passed through tissue. The conventional coating which has been used to coat the surfaces of needles for many years is silicone, which is not bioabsorbable. Another example are surgical sutures. Surgical sutures often require coated surfaces to improve the ease with which the surgeon can run a knot down the suture to anchor the suture at the site of surgical trauma.
Additionally, the development of biomedical polymers for the fabrication of surgical articles, devices and coatings, has emerged as an area of particular emphasis in the advancement and improvement in the medical and surgical arts. Much work has been documented on the increasing use of polymers in the medical profession. These polymers exhibit a wide range of physical and biological properties for numerous applications.
One of the driving forces behind the development of medical-grade polymers is the need to replace metallic components of various biomedical devices, which must often be removed from the body following surgery, with bioabsorbable polymers that need not be removed from the body following surgery. However, the requirements for suitable polymer replacements of metallic components are quite strenuous--the polymer must come close to or match the physical properties of the substituted metal.
By far, the most widely used polymers for medical applications are those derived from lactone monomers. Correspondingly, a wealth of research has arisen to create novel polymer systems derived from new lactone monomer compositions. This has lead to the development of lactone-based polymers with a wide range of properties for different applications. See, for example, U.S. Pat. Nos. 4,624,256; 4,788,979; 4,994,074; 5,007,923; 5,019,094; 5,037,950; 5,047,048; 5,076,807; and 5,133,739.
Another component which is used in making polymers, although not widely used for making biomedical polymers, is castor oil. Castor oil is known as a lubricating oil, and therefore has found wide-spread use for coating applications. See, for example, U.S. Pat. No. 3,461,093, which describes a copolymer of castor oil and a mixture of ethylenically unsaturated monomers, such as .alpha.-methylstyrene and a hydroxyalkyl methacrylate. In addition, there have been limited reports of the use of castor oil to prepare polymers for medical and surgical applications. In this regard, Canadian Patent 1,260,488 describes copolymers of a predominant amount of glycolide or lactide (or a mixture of these), and castor oil. The copolymers are said to have a wax-like consistency, and therefore are ideally suited for use in bone wax formulations for the control of bleeding from cut bone surfaces. It is also known to use castor oil as an initiator in the bulk polymerization of lactone monomers, e.g. glycolide, to prepare monofilament surgical threads. Similarly, Japanese Patent 2,055,717 describes the use of an emulsion containing a castor oil component as a lubricant oil for thermoplastic filaments.
While the polymer systems described above all provide particular properties for well-targeted applications, a need still exists to develop biomedical polymers which have enhanced lubricity and pliability for numerous applications, particularly for the preparation of polymer coatings for the surface of surgical articles. This increase in lubricity would be especially worthy if it could be obtained without sacrificing the processability of the polymer for making surgical articles or coatings for such articles. Finally, these goals would be further enhanced if they could be achieved with a polymer which is bioabsorbable, and therefore could truly be considered a suitable replacement for metallic components in numerous surgical devices.